Drive assisting system

ABSTRACT

An object of the present invention is to provide a driving assistance system capable of displaying a picked-up image near a vehicle as a less-distorted image on a monitor. 
     A driving assistance system according to the present invention comprises an imaging means ( 2 ) for picking up a surrounding image of a vehicle ( 1 ) on a road surface, an image translating means ( 3 ) for executing an image translation by using a three-dimensional projection model ( 300 ), which is convex toward a road surface side and whose height from the road surface is not changed within a predetermined range from a top end portion of the vehicle ( 1 ) in a traveling direction, to translate the image picked up by the imaging means ( 2 ) into an image viewed from a virtual camera ( 2   a ), and a displaying means ( 4 ) for displaying an image translated by the image translating means ( 3 ). The three-dimensional projection model ( 300 ) is configured by a cylindrical surface model ( 301 ) that is convex toward the road surface side, and a spherical surface model ( 302 ) connected to an end portion of the cylindrical surface model ( 301 ). Accordingly, the straight line on the road surface, which is in parallel with the center axis of the cylindrical surface model ( 301 ), is displayed as the straight line, and thus a clear and less-distorted screen can be provided to the driver.

TECHNICAL FIELD

The present invention relates to a driving assistance system whichassists when a vehicle backs by displaying a vehicle rear-side imagepicked up by a camera equipped with the vehicle on a monitor equippedwith the vehicle and, more particularly, to a driving assistance systemwhich displays a less distorted image on the equipped monitor therebynot causing a driver to feel a sense of incompatibility.

BACKGROUND ART

A driving assistance system which installs an equipped camera backwardin a rear trunk portion or the like of a vehicle and provides an imageof a rear side of the vehicle picked up by the equipped camera to thedriver is spreading nowadays. Some of the driving assistance systemstranslates/synthesizes a real image picked up the equipped camera intoan image that looks as if such image is picked up from a viewpoint beingset virtually and displays a resultant image on a monitor, and thedriving assistance systems are mainly used for the purpose of the safetycheck and the parking assistance in backing the vehicle.

As a three-dimensional projection model used to synthesize/translate theimage, for example, as shown in FIG. 10, a three-dimensional projectionmodel 100 configured to have a cylindrical surface model 101 and a flatsurface model 102 is used. Then, a real image picked up by a real camera103 is translated/synthesized into an image viewed from a virtual camera104, and then is displayed as an image projected onto thethree-dimensional projection model 100 on an equipped monitor.

FIG. 11 is an explanatory view showing an image obtained by projecting astraight line 105 shown in FIG. 10 onto the three-dimensional projectionmodel 100. A straight line image 105 a on a monitor screen 106 isdisplayed to be folded at a model boundary 107 between the cylindricalsurface model 101 and the flat surface model 102. In this manner, thereason for that originally straight line 105 is translated as a foldedimage 105 a when the three-dimensional projection model 100 configuredto combine the cylindrical surface onto which the far image is projectedand the flat surface onto which the near image is projected is used isthat distortion of the display is concentrated onto the model boundary107 between two three-dimensional projection models 101, 102. Thus, whenthe driver looks at this folded image 105 a, he or she perceives a senseof incompatibility.

Therefore, if two three-dimensional projection models are smoothlyconnected by a curved surface (third three-dimensional projectionmodel), the straight line image 105 a is smoothly curved, as shown inFIG. 12, and it is possible to relax the sense of incompatibility.However, since the distortion is concentrated onto a projection surface108 onto the third three-dimensional projection model, a sense ofincompatibility still remains.

Therefore, in the prior art set forth in JP-A-2002-83285, for example,the three-dimensional projection model shown in FIG. 13 is proposed.This three-dimensional projection model 200 is configured to have thecylindrical surface 101 onto which the far image is projected, and aspherical surface model 201 which is successively connected to thissurface and onto which the near image is projected. In this manner,since the spherical surface model 201 is used as the model on which thepicked-up image near the vehicle is projected, an overall projectedimage on the spherical surface model 201 changes smoothly and thereforea sense of incompatibility of the driver can be considerably relaxed.

However, if the above three-dimensional projection model 200 shown inFIG. 13 is used, the picked-up image near the vehicle is never distortedat the particular portion concentrated, but it occurs a problem that thedistortion is generated in the overall image. For example, the imageobtained by picking up an image of a lattice pattern on the ground 202by the real camera 103 and then projecting the picked-up image onto thespherical surface model 201 is distorted as a whole, as shown in FIG.14. That is, there is a problem such that a group of straight linesconstituting originally a lattice on the ground 202 are displayed as agroup of curved lines on the screen 106, and it is difficult to grasppositional relationships between the driver's own vehicle and thesurroundings based on such image.

An object of the present invention is to provide a driving assistancesystem in which a three-dimensional projection model capable ofmonitoring/displaying a surrounding image of a vehicle as a lessdistorted image while suppressing incompatibility with a distant imagefrom the vehicle is installed.

DISCLOSURE OF INVENTION

In order to attain the above object, a driving assistance system of thepresent invention has imaging means for picking up a surrounding imageof a vehicle on a road surface; image translating means for executing animage translation by using a three-dimensional projection model, inwhich a shape on a side of the road surface is convex and a height fromthe road surface does not vary within a predetermined range from a topend portion of the vehicle in a traveling direction, to translate theimage picked up by the imaging means into an image viewed from a virtualviewpoint; and displaying means for displaying an image translated bythe image translating means.

According to this configuration, in the driving assistance system of thepresent invention, the straight line such as the box of the parking lot,or the like depicted in parallel with the traveling direction of thevehicle on the road surface near the vehicle is displayed as thestraight line on the screen of the displaying means, and thus it becomeseasy to grasp the relative positional relationship between the driver'sown vehicle and the surroundings.

Preferably, a projection surface that gradually gets up from the roadsurface in a range extending beyond the predetermined range in a widthdirection of the vehicle is continuously provided in thethree-dimensional projection model. According to this configuration, thepicked-up image in a wide range in the width direction of the vehiclecan be displayed on the screen not to make the image distortionprominent.

Preferably, a projection surface that gradually gets up from the roadsurface in a range extending beyond the predetermined range in thetraveling direction of the vehicle is continuously provided in thethree-dimensional projection model. According to this configuration, thepicked-up image in a wide range in the traveling direction of thevehicle can be displayed on the screen not to make the image distortionprominent.

More preferably, the three-dimensional projection model is formed bysuccessive curved surfaces that can be differentiated in a full rangeexcept end points. According to this configuration, no discontinuoussingular point is present on the screen, and a sense of incompatibilitycaused by connecting a plurality of three-dimensional models (thecylindrical surface and the spherical surface) is not generated. Also, ascale factor or a distortion can be varied on the screen by adjusting aninclination of the convex surface, and thus a sense of distance and asense of direction on the screen can be adjusted by utilizing this. Inaddition, since all three-dimensional models are a smooth curved surfacethat is convex downward, the image distortion is not concentrated into aparticular portion but dispersed over the entire screen to provide aclear screen. Therefore, the image by which the driver easily grasps thesense of distance and from which the driver does not feel a sense ofincompatibility can be provided to the driver.

More preferably, the three-dimensional projection model has acylindrical surface which shape on the side of the road surface isconvex, and a spherical surface which is smoothly connected to an endportion of the cylindrical surface. According to this configuration, thethree-dimensional projection models can be represented by equations, andthus the image translating process and formation of the mapping tablecan be made easy.

More preferably, the predetermined range is projected onto thecylindrical surface to has a length in the traveling direction of thevehicle, which is set to 120% or less of 5 m that is a length of anormal box of a parking lot, and a width, which is set to a range of 80%to 120% of 3 m that is a width of the normal box of the parking lot.According to this configuration, the screen that is suited to theparking operations can be provided to the driver.

More preferably, the cylindrical surface is a cylindrical surface of anellipse, and the ellipse whose ratio of a maximum width and a minimumwidth between equal-interval lattice lines, which are in parallel with acenter axis of the cylindrical surface on the road surface projectedonto the cylindrical surface, is at least 80% in the predetermined rangeis used as the three-dimensional projection model. According to thisconfiguration, the screen that has a small distortion can be provided tothe driver.

More preferably, the three-dimensional projection model and a positionof the virtual viewpoint are set such that both left and right ends of arear end image of the vehicle displayed on a screen of the displayingmeans enter into an at least 15% range of a screen width from both endpositions of the screen. According to this configuration, the image ofthe blind spot position, which cannot be directly viewed by the driver,is displayed largely on the screen, and thus the driver can drive with asense of security.

More preferably, the three-dimensional projection model and a positionof the virtual viewpoint are set such that a linear shape of a rear endof the vehicle in the predetermined range is displayed as a linear imageon the screen of the displaying means. According to this configuration,the driver can easily confirm a shape of a bumper, etc. of the driver'sown vehicle, and the driver can exactly grasped the positionalrelationship between the road surface and the driver's own vehicle. Inaddition, since positions of the three-dimensional projection model andthe virtual viewpoint are set such that left and right both ends of therear end image of the vehicle displayed on the screen on the displayingmeans enter into an at least 15% range off the screen width from bothend positions of the screen, the image of the rear portion of thevehicle such as the bumper, etc., which is displayed larger than a widthof the vehicle on the road surface on the screen obtained by the viewingtranslation, is cut off to have an appropriate width in response to thewidth of the screen and then displayed. Therefore, it is possible toreduce a factor of the sense of incompatibility such that a width of thevehicle on the road surface and a width of the bumper are largelydifferently displayed.

More preferably, a guide line indicating a straight line on the roadsurface, which is in parallel with the traveling direction of thevehicle and indicates an outer side that is outer than the width of thevehicle by a predetermined value, is superposed on an image translatedby using the three-dimensional projection model and to display on thescreen of the displaying means. According to this configuration, thedriver can intuitively catch the relative positional relationshipbetween the guide line and the straight line on the road surface fromthe screen, and thus the operation of aligning the position to the marksuch as the side line of the box of the parking lot, the road surface,etc. in the parking is made easy.

More preferably, the image translating means translates the picked-upimage by using a mapping table in which a translation address based onthe three-dimensional projection model is stored. According to thisconfiguration, it is not required to execute the computing process byusing the three-dimensional projection model every time, and thus theimage translating process can be carried out at a high speed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configurative view showing a fitting of a driving assistancesystem according to an embodiment of the present invention to a vehicle;

FIG. 2 is a configurative view showing details of the driving assistancesystem according to the embodiment of the present invention;

FIG. 3 is a schematic view showing an image of a wide-angle camerapicked up by an imaging device in the driving assistance systemaccording to the embodiment of the present invention;

FIG. 4 is a schematic view showing an image obtained by eliminating alens distortion from the image of the wide-angle camera picked up by theimaging device in the driving assistance system according to theembodiment of the present invention;

FIG. 5 is a schematic view showing a monitor display screen by thedriving assistance system according to the embodiment of the presentinvention;

FIG. 6 is a schematic view showing a variation of the monitor displayscreen by the driving assistance system according to the embodiment ofthe present invention;

FIG. 7 is an explanatory view showing a three-dimensional projectionmodel used in the driving assistance system according to the embodimentof the present invention;

FIG. 8 is an explanatory view showing a three-dimensional projectionmodel according to the embodiment of the present invention;

FIGS. 9A to 9C are explanatory views showing an example of an imagetranslated by the three-dimensional projection model according to theembodiment of the present invention;

FIG. 10 is an explanatory view showing a three-dimensional projectionmodel used in the driving assistance system in the prior art;

FIG. 11 is a schematic view showing an image translated by thethree-dimensional projection model used in the driving assistance systemin the prior art;

FIG. 12 is a schematic view showing a variation of the translated imageby the driving assistance system in the prior art;

FIG. 13 is an explanatory view showing another three-dimensionalprojection model used in the driving assistance system in the prior art;and

FIG. 14 is a schematic view showing an image distortion caused by thethree-dimensional projection model in FIG. 13 used in the drivingassistance system in the prior art.

In Figures, a reference numeral 1 is an own vehicle, 1 a is a bumperimage, 2 is an imaging device, 3 is an image synthesizing translatingsystem, 4 is a display device (monitor), 10 is a distance-indicatingguide line, 11 is a width indicating guide line, 12 is a linear guideline on a road surface, 21, 23 are cameras, 22, 24 are frame memories,31 is an image synthesizing means, 32 is a mapping table looking-upmeans, 32 a is a translation address memory, 32 b is adegree-of-necessity memory, 33 is an image signal generating means, 300is a three-dimensional projection model, 301 is a cylindrical surfacemodel (ellipse), 302 is a spherical surface model (ellipse), 506 is aflat surface model, and 521, 522 are cylindrical surface models.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be explained with referenceto the drawings hereinafter.

FIG. 1 is a configurative view showing a fitting of a driving assistancesystem according to an embodiment of the present invention to a vehicle.This driving assistance system is configured to have an imaging device 2provided in a vehicle 1, an image synthesizing translating system 3which processes an image picked up by the imaging device 2, and amonitor 4 which displays an image that was subjected to the imagesynthesizing translating process.

The imaging device 2 is provided to pick up an image of the rear of thevehicle 1. A lens distortion is eliminated from the image acquired fromthe imaging device 2 by the image synthesizing translating system 3, andthe image is translated into an image that looks as if such image ispicked up from any virtual viewpoint to display the image on the monitor(displaying means) 4.

FIG. 2 is a configurative view showing details of the driving assistancesystem. The imaging device 2 includes a camera 21 provided to pick up animage of the left-side area on the back side of the vehicle, a framememory 22 which temporarily holds image data obtained from the camera21, a camera 23 provided to pick up an image of the right-side area onthe back side of the vehicle, and a frame memory 24 which temporarilyholds image data obtained from the camera 23. In the present embodiment,the left side and right side on the back side of the vehicle are pickedup by the cameras 21, 23 respectively and then left and right picked-upimages are synthesized. But, the left side and right side on the backside of the vehicle might be picked up by one camera at a time.

The image synthesizing translating system 3 is configured to have animage synthesizing means 31 which synthesizes left-side and right-sideimages on the back side of the vehicle read from two frame memories 22,24 of the imaging device 2, a mapping table looking-up means 32 whichstores mapping information of respective pixels of the image that issynthesized by the image synthesizing means 31, and an image signalgenerating means 33 which translates the image synthesized by the imagesynthesizing means 31 into an image signal.

The mapping table looking-up means 32 includes a translation addressmemory 32 a which stores translation addresses (a mapping table)indicating correspondences between positional coordinates of respectivepixels of an output image (an image displayed on the monitor 4) andpositional coordinates of respective pixels of input images (imagespicked up by the cameras 21, 23), and a degree-of-necessity memory 32 bwhich stores degrees-of-necessity of respective pixels of the inputimages.

Here, a “degree-of-necessity” is a value to calculate of addition when asheet of output image is generated by connecting left-side andright-side input images, for example, such that a degree-of-necessity ofthe right-side input image is “0.5”, a degree-of-necessity of theleft-side input image is “0.5”, etc. when values of respective pixeldata of the area where the left-side and right-side input imagescombines each other are to be decided. Also, the above translationaddresses are previously generated on the basis of the three-dimensionalprojection model described later in detail, and stored in thetranslation address memory 32 a.

The image synthesizing means 31 generates data of the output pixels bysynthesizing respective pixel data in the frame memories 22, 24 bymixers 31 a, 31 b according to the designated degree-of-necessity basedon the translation addresses (the mapping table) recorded in the mappingtable looking-up means 32, and then adding the synthesized left-side andright-side pixel data by an adder 31 c.

That is, the image synthesizing means 31 operates based on anappropriate synchronizing signal such as the input image signal, or thelike, for example, generates the output image by synthesizing the imagesinput from two different cameras 21, 23 in accordance with the mappingtable looking-up means 32 or changing respective pixel positions, andthus connects the input images input from plural different cameras 21,23 in real time or translates the input images into an image viewed fromthe virtual viewpoint.

The image signal generating means 33 translates output pixel data outputfrom the image synthesizing means 31 to the image signal, and outputsthe signal to the monitor 4.

The translation addresses stored in the mapping table looking-up means32 are generated based on the three-dimensional projection modelaccording to the present embodiment. This three-dimensional projectionmodel is a model indicating correspondences when the images picked up bythe cameras 21, 23 are translated to the image that looks as ifsuch-image is picked up by the virtual camera which is installed at avirtual viewing position.

Actually, the cameras 21, 23 are wide-angle camera. The image on therear side of the vehicle, which can be obtained by synthesizing thepicked-up images laterally, is displayed as larger as the image iscloser to the vehicle and is displayed as smaller as the image isfurther from the vehicle, as shown in FIG. 3. The illustrated exampleshows the image of a parking area (normally a rectangular area whosevertical dimension is almost 5 m and whose lateral dimension is almost 3m is shown. This parking area is indicated by a lattice pattern to beeasy to understand.) of the rear of the vehicle, which is picked up bythe wide-angle camera. In the present embodiment, as shown in FIG. 5 andFIG. 6, the image in FIG. 3 is displayed on the monitor 4 as the clearand less-distorted image by the translation addresses generated by usingthe three-dimensional projection model described later.

FIG. 7 is a view showing a three-dimensional projection model used inthe present embodiment. A three-dimensional projection model 300 used inthe present embodiment is configured to include a cylindrical surfacemodel 301 on which the far image is projected, and a spherical surfacemodel 302 which is connected smoothly to the cylindrical surface model301 and on which the near image is projected. An alignment direction ofthis three-dimensional projection model 300 is different from theconventional three-dimensional projection model 200 explained in FIG.13. That is, the present embodiment is characterized in that an axis ofthe cylindrical surface model 301 is arranged in parallel with theground (road surface), i.e., the traveling direction of own vehicle 1,and a lower convex surface of the cylindrical surface model 301 isarranged on the ground side.

The imaging device 2 installed in the own vehicle 1 to pick up thebackward image picks up the backward image in the axial direction of thethree-dimensional projection model 300. The image synthesizingtranslating system 3 translates the picked-up image picked up by theimaging device 2 into the image that looks as if such image is picked upby a virtual camera 2 a, which is installed over the actual imagingdevice 2, through the three-dimensional projection model 300, and thendisplays the image on the monitor 4.

The cylindrical surface model 301 of the three-dimensional projectionmodel 300 is a semi-spherical model that is installed on the roadsurface such that a center axis of the cylindrical surface model 301 isin parallel with the traveling direction of the vehicle and is cut inhalf by a flat surface that passes through the center axis of thecylindrical surface model 301 in parallel with the road surface. Thespherical surface model 302 is a spherical surface whose radius isidentical to a radius of the cylindrical surface model 301, whose centeris on the center axis of the cylindrical surface model 301, and whosecut end formed by cutting the sphere by a plane, which passes throughthe center and has the center axis of the cylindrical surface model 301as a perpendicular, perfectly coincides with the cylindrical surfacemodel 301. That is, the cylindrical surface model 301 and the sphericalsurface model 302 can be differentiated at all points (except endpoints) on the boundary.

For convenience of explanation, the above three-dimensional projectionmodel 300 is explained as a “circular cylinder” and a “sphere”. But themodel is not always be a perfect “circular cylinder” and a perfect“sphere”, and may be as an ellipse, an elliptic sphere respectively. Forexample, the ellipse that is oblate on the road surface side may beselected as the three-dimensional projection model. A view showing bythe three-dimensional projection model consisting of this ellipse, whichis cut by a flat plane perpendicular to the traveling direction of thevehicle 1, is FIG. 8. In this case, FIG. 8 shows not only the lower halfof the ellipse constituting the model but also an overall ellipse.

Three three-dimensional projection models are shown in FIG. 8. One modelis a flat surface model 506 whose direction coincides with the roadsurface, and the other two models are elliptic models 521, 522 whoseellipticity is respectively different (the portion corresponding to thethree-dimensional projection model 301 in FIG. 7). Only a length of aminor axis is different between the elliptic models 521, 522. Viewsobtained by picking up an image of a lattice pattern, which is depictedon the road surface at an equal interval, by the imaging device 2 shownin FIG. 7, and then translating the image into an image that looks as ifsuch image is picked up by the virtual camera 2 a shown in FIG. 7through three models 506, 521, 522 shown in FIG. 8 are FIGS. 9A-9Crespectively. In this case, these images are picked up when the virtualcamera 2 a is directed just downwards.

As shown in FIG. 8, assume that an axis that is in parallel with thecenter axes of the cylindrical surfaces of the ellipses 521, 522 and ispositioned on the road surface is set as a Y axis, an axis thatintersects orthogonally with the Y axis and is perpendicular to the roadsurface is set as a Z axis, and an axis that intersects orthogonallywith the Y axis and the Z axis is set as an X axis, their values on theY axis are the same in respective models 506, 521, 522, but theirheights become different (values on the Z-axis direction) as theposition becomes more distant from the Y axis in the X-axis direction.

In other words, out of the lattice pattern depicted on the road surface,the lines that are in parallel with the Y axis are also depicted asparallel lines on the screens that are translated with using respectivemodels 506, 521, 522. In the model 522 having a small ellipticity, i.e.,in which a position goes away from the road surface as the positionbecomes more distant in the X-axis direction, an interval x2 of thelattice pattern on the end side of the screen becomes narrower than aninterval x1 of the lattice pattern around the center, as shown in FIG.9C.

Therefore, in the three-dimensional projection model 300 (thecylindrical surface model 521 of the ellipse shown in FIG. 8 is used asthe cylindrical surface model 301 of the actually used model 300, andthe spherical surface model of the ellipse being continued smoothly tothe cylindrical surface model 521 of the ellipse is used as thespherical surface model 302) used in the present embodiment, it isdecided as follows to what extent the ellipticity of the ellipse that isused as the cylindrical surface model 521 should be set.

That is, the X axis shown in FIG. 8 corresponds to the width directionof own vehicle 1 shown in FIG. 7. Therefore, any range 503 is taken outfrom a range of 80% to 120 of 3 m which is a width of a normal box of aparking lot having the Y axis as its center. Then, the three-dimensionalprojection model 521 of the ellipse is set such that a ratio of amaximum value Xmax and a minimum value Xmin of the interval of thelattice pattern, which is formed at an equal interval on the roadsurface, is at least 80% or more, as shown in FIG. 9B, within the imagethat is subjected to the translation through the three-dimensionalprojection model 521 contained in this range 503.

Such three-dimensional projection model 521 can be easily set byadjusting lengths of a major axis and a minor axis of the ellipse.,Views obtained by deciding the cylindrical surface model 301 in FIG. 7based on the ellipse in this manner and displaying the translated imageof the lattice pattern are FIG. 5 and FIG. 6. In these translatedimages, the straight line extending in the same direction as thetraveling direction of own vehicle 1 is also displayed as the straightline in the translated image, and the image distortion in the translatedimage along the width direction can be suppressed into the gentledistortion to such an extent that the driver does not feel a sense ofincompatibility.

In the driving operations of the vehicle, since the straight lines suchas the side line of the road, the side line of the box of the parkinglot, etc., which are in parallel with the Y axis, are often used as amark, it is a big advantage in the driving operations that the straightline along the Y axis can also be displayed as the straight line in thetranslated image. In the present embodiment, since the cylindricalsurface model 301 is employed as the model on which the picked-up imageof the road surface is projected, the straight line is translated intothe straight line. As a result, the present embodiment can enjoy thisadvantage.

Meanwhile, in a far range 504 that extends in the width direction beyondthe range 503 shown in FIG. 8, if the picked-up image is projected ontothe flat surface, a solid body is largely distorted and thus the driverfeels strange. Therefore, in order to reduce this image distortion, itis preferable that the projecting surface should be set as a surfacethat gets up from the road surface. However, if this projecting surfaceis set to a surface that suddenly gets up from the cylindrical surfacemodel 301, the image distortion is concentrated onto the boundaryportion. Therefore, it is preferable that the projecting surface gettingup gradually should be selected. Since the elliptic model 521 graduallygets up in the range 504, the image distortion can be dispersed over theentire screen by using this elliptic model 521 in the range 504.Therefore, it is feasible to provide the translated image that causesthe driver to feel less a sense of incompatibility.

This is similarly true of the Y-axis direction. If the far picked-upimage in the Y-axis direction is projected onto the flat surface, thesolid body is largely distorted and thus the driver feels strange.Therefore, it is also needed in the Y-axis direction that the projectingsurface is caused to get up in the far range. Since the Y-axis directioncorresponds to the traveling direction of the vehicle, i.e., thelongitudinal direction of the vehicle, the image translation is executedin a predetermined range from the rear end of the vehicle by using themodel 521 whereas the image translation is executed in a range, whichextends beyond the predetermined range from the rear end of the vehicle,by using the elliptic sphere (the model 302 in FIG. 7) continued fromthe model 521.

Since the normal box of a parking lot is 5 m in length, it is desiredthat this predetermined range in the Y-axis direction should be set anyvalue in 80% to 120% of a 5 m range. Also, it is preferable that noinclination is provided to the Y-axis direction in this predeterminedrange. In the cylindrical surface model 301 of the three-dimensionalprojection model 300 according to the present embodiment, a height ofthe lowermost position from the road surface is set to zero (coincideswith the road surface) over the length of the cylindrical surface model301. Accordingly, the straight line in the picked-up image in thepredetermined range is also displayed as the straight line in thetranslated image.

However, in many case almost a half of the picked-up image by theimaging device 2 shown in FIG. 7 is located within an about 2 m rangefrom the rear portion of the vehicle. In such image, it is not alwaysneeded to keep above 5 m. An inclination may not be provided to theY-axis direction only within the 2 m range in which a sufficient spaceresolution is achieved, but the inclination may be gradually increasedin a range extending beyond 2 m, like the X-axis direction.

In the translated images in FIG. 5 and FIG. 6 according to the presentembodiment, the straight line is displayed as the straight line on thisside of a distance-indicating guide line 10 indicating the 2 m rangefrom the rear portion of the vehicle, while the image translation iscarried out by using the elliptic sphere model 302 in the rangeextending beyond 2 m. The predetermined range is different according tothe installation position of the imaging device 2, the resolution, theposition of the virtual viewpoint, etc. In this case, it is desired froma point of view of the driving assistance that the ellipse model 301should be applied in the box of the parking lot range from the rear endof the vehicle 1, which is selected as the predetermined range, and alsothe elliptic sphere model 302 should be applied in the farther range.

In the present embodiment, the three-dimensional projection model isconfigured with the cylindrical surface model 301 as the ellipse and thespherical surface model 302 as the ellipse. Accordingly, the cylindricalsurface model 301 as the ellipse and the spherical surface model 302 asthe ellipse are continuously coupled. As a result, as shown in FIG. 5and FIG. 6, the translated image is smoothly connected in the boundarysurface between the model 301 and the model 302 of the three-dimensionalprojection model 300. Thus, the driver cannot discriminate the boundaryand never perceive a sense of incompatibility.

As described above, an extent of image distortion of the solid body inthe range 504 can be adjusted by adjusting the inclination of theprojection model in this range 504 shown in FIG. 8. For example, asshown in FIG. 5, if an appropriate inclination is provided to theprojection model in the range 504, a distortion level of the imagepicked up by the imaging device using a wide-angle lens can be adjusted,so that a scale factor of other vehicle in a distant place can be set toget the sense of distance obtained when the driver actually looks out ofthe rear window.

FIG. 4 illustrated by way of comparison shows the image of a wide-anglelens in FIG. 3 from which a lens distortion of the wide-angle lens iseliminated. It is appreciated that, even though only the lens distortionis eliminated, an effect of emphasizing the sense of distance by usingthe wide-angle lens is not relaxed. That is, a distant image looks moredistant, the sense of distance is still emphasized in the image. Incontrast, in the present embodiment, since the far image is translatedby using the elliptic sphere model 302, the sense of distance is relaxedto provide a clear image, as shown in FIG. 5.

If the major axes and the minor axes of the cylindrical surface model301 and the elliptic sphere model 302 in FIG. 7 and the viewing positionof the virtual camera 2 a are adjusted, the image shown in FIG. 5 can betranslated into the image shown in FIG. 6 and then displayed on themonitor 4. That is, a width d of the own vehicle 1 on the road surfacecan be displayed on the screen in an enlarged fashion. In this FIG. 6,the image shown in FIG. 5 is translated and displayed such that both endpositions of the vehicle enter into a 15% range of the screen width fromboth end positions of the screen.

According to such enlarged display, the image near the rear end of theown vehicle 1, which is a blind spot of the driver, is displayed fullyon the screen of the monitor 4. Therefore, it gives the driver a senseof security. As a result, the driver can perform the driving operationswith a sense of security.

Similarly, if the major axes and the minor axes of the ellipses of thecylindrical surface model 301 and the elliptic sphere model 302 in FIG.7 and the position of the virtual camera 2 a are adjusted, a bumperimage 1 a of the own vehicle 1 can be displayed as the straight line, asshown in FIG. 5 and FIG. 6. Compared with that the bumper image 1 a isdisplayed in curve, as shown in FIG. 3 or FIG. 4, the driver feels asense of less-incompatibility to do the driving operations easily.

In addition, in the present embodiment, as shown in FIG. 6, for example,a mark 11 indicating a width of the vehicle and a guide line 12corresponding to a straight line on the road surface, which indicates aside that is in parallel with the traveling direction of the vehicle andis positioned slightly outer than the width d of the vehicle, aredisplayed. According to these displays, the driver can intuitively graspthe mutual positional relationship between the side line of the road orthe box of the parking lot and the driver's own vehicle from the screento assist the exact driving operation.

In this case, the above three-dimensional projection model configuredwith the cylindrical surface model and the spherical surface model isnot always configured by the curved surfaces that are defined by theequations, and decided based on the application range and the property.For example, the cylindrical surface model 301 as the ellipse is notalways shaped into the elliptic shape in compliance with the ellipticequation. The three-dimensional projection model that is convexdownwards and is shaped to disperse the distortion of thetranslated-image over the entire image may be employed. The same isapplied to the spherical surface model 302.

The present invention is explained in detail with reference to theparticular embodiment. But it is obvious for the person skilled in theart that various variations and modifications may be applied withoutdeparting a spirit and a scope of the present invention.

This application was made based on Japanese Patent. ApplicationNo.2002-171484 filed on Jun. 12, 2002, and the content thereof isincorporated hereinto by the reference.

INDUSTRIAL APPLICABILITY

According to the present invention, it is feasible to provide thedriving assistance system that is capable of monitoring/displaying thesurrounding image of the vehicle as the less-distorted image.

1. A driving assistance system comprising: imaging means for picking upa surrounding image of a vehicle on a road surface; image translatingmeans for executing an image translation by using a three-dimensionalprojection model, in which an object outside of said vehicle on a sideand above of the road surface is picked up by said imaging means and animage of said object is projected as a convex curve and a height fromthe road surface of said image of said object does not appear to varyfrom an image of a different object of a similar height when thedifferent object is within a predetermined range from a top end portionof the vehicle in a traveling direction, to translate the image pickedup by the imaging means into an image viewed from a virtual viewpoint;and displaying means for displaying the image translated by the imagetranslating means, wherein the three-dimensional projection model has acylindrical surface on which a shape on the side of the road surface isprojected as a convex curve, and a spherical surface which is smoothlyconnected to an end portion of the cylindrical surface, wherein saidcylindrical surface has an axis that is parallel with the road surfacefor some substantial length.
 2. The driving assistance system accordingto claim 1, wherein a projection surface that gradually gets up from theroad surface in a range extending beyond the predetermined range in awidth direction of the vehicle is continuously provided in thethree-dimensional projection model.
 3. The driving assistance systemaccording to claim 1, wherein a projection surface that gradually getsup from the road surface in a range extending beyond the predeterminedrange in the traveling direction of the vehicle is continuously providedin the three-dimensional projection model.
 4. The driving assistancesystem according to claim 1, wherein the three-dimensional projectionmodel is formed by successive curved surfaces that can be differentiatedin a full range except end points.
 5. The driving assistance systemaccording to claim 4, wherein the predetermined range is projected ontothe cylindrical surface having a length in the traveling direction ofthe vehicle, which is set to 120% or less of 5 m that is a length of anormal box of a parking lot, and having an arbitrary width, which is setto a range of 80% to 120% of 3 m that is a width of the normal box ofthe parking lot.
 6. The driving assistance system according to claim 5,wherein the cylindrical surface is a cylindrical surface of an ellipse,and the ellipse whose ratio of a maximum width and a minimum widthbetween equal-interval lattice lines, which are in parallel with acenter axis of the cylindrical surface on the road surface projectedonto the cylindrical surface, is at least 80% in the predetermined rangeis used as the three-dimensional projection model.
 7. The drivingassistance system according to any one of claim 4, wherein thethree-dimensional projection model and a position of the virtualviewpoint are set such that both left and right ends of a rear end imageof the vehicle displayed on a screen of the displaying means enter intoan at least 15% range of a screen width from both end positions of thescreen.
 8. The driving assistance system according to claim 4, whereinthe three-dimensional projection model and a position of the virtualviewpoint are set such that a linear shape of a rear end of the vehiclein the predetermined range is displayed as a linear image on the screenof the displaying means.
 9. The driving assistance system according toclaim 1, wherein a guide line indicating a straight line on the roadsurface, which is in parallel with the traveling direction of thevehicle and indicates an outer side that is outer than the width of thevehicle by a predetermined value, is superposed on an image translatedby using the three-dimensional projection model to display on the screenof the displaying means.
 10. The driving assistance system according toclaim 1, wherein the image translating means translates the picked-upimage by using a mapping table in which a translation address based onthe three-dimensional projection model is stored.
 11. A drivingassistance system comprising: imaging means for picking up a surroundingimage of a vehicle on a road surface; image translating means forexecuting an image translation by using a three-dimensional projectionmodel, in which an object outside of said vehicle is picked up by saidimaging means and an image of said object is projected as a convex curvecomprised of at least part of a ellipsoid surface model smoothlyconnected to at least part of a cylindrical surface model having acylindrical axis that is parallel with the road surface for somesubstantial length; and displaying means for displaying the imagetranslated by the image translating means.
 12. The system of claim 11,wherein said substantial length is at least 3 meters.
 13. The system ofclaim 11, wherein said cylindrical surface model has an elliptical crosssection.
 14. The system of claim 11, wherein said ellipsoid isspherical.
 15. A driving assistance system comprising: imaging means forpicking up a surrounding image of a vehicle on a road surface; imagetranslating means for executing an image translation by using athree-dimensional projection model, in which an object outside of saidvehicle on a side of the road surface is picked up by said imaging meansand an image of said object is projected as a convex curve comprised ofat least part of a quadric surface model smoothly connected to at leastpart of a cylindrical surface model having a cylindrical axis that isparallel with the road surface for at least three meters, such that aheight from the road surface of said image of said object does notappear to vary from an image of a different object of a similar heightwhen the different object is within a predetermined range from a top endportion of the vehicle in a traveling direction, to translate the imagepicked up by the imaging means into an image viewed from a virtualviewpoint; and displaying means for displaying the image translated bythe image translating means.
 16. The system of claim 15, wherein saidcylindrical surface model has an elliptical cross section.
 17. Thesystem of claim 15, wherein said ellipsoid is spherical.